I may be opening a can of worms here... but, what kind of engine oil are you using? Several articles listed on the web talk about motorcycle oil being a rip off for the price. I've been using silkolene in my last 3 bikes including the Busa and have had zero problems. How about you guys?
MOBIL MX4T, very good results. The debate on price I really don't care (not that I am rich with 2 kids in college) but the amount is minimal @ $7.59 per quart. Some say that the 15w50 will get you the same @ $4.00 per quart but i don't want to risk the change. MX4T is very difficult to find in my area, I have to get it about 25 miles away, so i buy the case.
I use Bel Ray EXS Synthetic Superbike oil. There are quite a few good oil manufacturers out there, and you normally get what you pay for. Motul makes a good oil, but it can be hard to find and sometimes costly. Whatever you do, make sure you use a quality motorcycle oil. There is a huge difference between car and bike oil. Car oils lubricate the inside of the engine the same as bike oils do, and cost less than half as much, which tempts a lot of bike owners. What you must realize is that bike oil also must lubricate the transmission and the clutch in your bike. If you use car oil, usually the first thing to happen will be a slipping/destroyed clutch. If you are easy on the clutch though, you will just wear your engine out. Oils have additives in them to do various jobs, the most important in bikes are the anti-shear additives. Picture an oil molecule as a piece of plastic. Not bad lubricating qualities, and the thickness or viscosity of the oil would relate to the size of the piece of plastic. In the engine the oil takes up the space between the moving parts so they don't touch each other, they ride on the film of oil. But the gears in the transmission will cut or shear the oil as it gets caught between them. If the pieces of plastic are cut in half enough times, pretty soon they are so thin they cannot take up the space between the engine parts and metal to metal contact occurs, causing wear.
Also, for much the same reason, most synthetic motorcycle oils use an esther base, which I believe is an organic oil base (like vegetable oil) wheras most car synthetics are petroleum based. The esther base is much more costly to produce and has a lower demand so the prices are higher.
Synthetics are not the only way to go, but the synthetic base oil will accept more/better additives, and will maintain its viscosity over a wider temperature range. That is important to me as I live in a climate where the temperature will range from 40F when I start riding in the spring to 110+F in the middle of summer.
Everyone out there buys their polymers from Mobil so don't waste your money on expensive motorcycle specific oil. Mobil One synthetic 15w50 will give excellent protection for your engine and transmission. I have used it in all my bikes including my Dragbike with no oil related failures. If it protects my dragbike a streetbike will never have a problem as the dragbike suffers more abuse than any streetbike will ever see...Knebnr
I have heard that one should use motorcycle specific oil from my friend who is a factory trained Suzuki Mech and I tend to believe him on this one. Mostly because of the wet clutch. He said to always check the label car oils have more detergents... but if you want to read another argument check out this story at www.yft.org/tex_vfr/tech/oil.htm
Oh and just changed to full synthetic as I was using a blend. Also changed coolant today and flushed rad. I was surprized at the amount of crap in the res bottle flushed it the longest. The radiator looked good. Bike has allmost 7K miles and is a 2000 model.
I used to use Silkolene but have used Castrol R4 Superbike fully synthetic for the last 12000 miles about £30- £32 for 4 litres ($40- 45). Fully Synthetic oil is all about the same price here except Motul 300V about £36.
Car oil is not suitable for bikes as in a car engine, oil only lubricates engine and does not have a wet clutch or the shearing action of gearbox lubrication.
No difference shifting is smooth. Polymers are the same in both oils the price on the mx4t is just incredibly expensive. I do full power launches on the Super Comp Dragbike and the shifting is flawless even under full load and this bike makes 200+hp..........................I have never had any problems with any bike I have used the 15w50 Mobil One in and I have a 91 zx11 in original condition engine still makes 132hp thats a pretty good testament to the Mobil One oil..............Knebnr